What Is a Spine-Leaf Architecture?

A quick primer on a spine-leaf topology and its benefits over traditional network designs.

Man working in the data center

A spine-leaf architecture is an increasingly popular data center network topology that consists of two switching layers—a spine and leaf. The leaf layer consists of access switches that aggregate traffic from servers—typically affixed top of rack (ToR) or end of rack (EoR)—and connect directly into the spine or network core. Spine switches interconnect all of the leaf switches in a full-mesh topology.

How does a spine-leaf architecture differ from traditional network designs?

Traditionally, data center networks were based on a three-tier model:

  1. Access switches connect to servers
  2. Aggregation or distribution switches provide redundant connections to access switches
  3. Core switches provide fast transport between aggregation switches, typically connected in a redundant pair for high availability

At the most basic level, a spine-leaf architecture collapses one of these tiers, as depicted in these diagrams.

Leaf-Spine Architecture diagram

Other common differences in spine-leaf topologies include:

  • The removal of Spanning Tree Protocol (STP)
  • Increased use of fixed port switches over modular models for the network backbone
  • More cabling to purchase and manage, given the higher interconnection count
  • A scale-out vs. scale-up of infrastructure

Why are spine-leaf architectures becoming more popular?

Given the prevalence of cloud and containerized infrastructure in modern data centers, east-west traffic continues to increase. East-west traffic moves laterally, from server to server. This shift is primarily explained by modern applications having components that are distributed across more servers or VMs.

With east-west traffic, having low-latency, optimized traffic flows is imperative for performance, especially for time-sensitive or data-intensive applications. A spine-leaf architecture aids this by ensuring traffic is always the same number of hops from its next destination, so latency is lower and predictable.

Capacity also improves because STP is no longer required. While STP enables redundant paths between two switches, only one can be active at any time. As a result, paths often become oversubscribed. Conversely, spine-leaf architectures rely on protocols such as Equal-Cost Multipath (ECPM) routing to load balance traffic across all available paths while still preventing network loops.

In addition to higher performance, spine-leaf topologies provide better scalability. Additional spine switches can be added and connected to every leaf, increasing capacity. Likewise, new leaf switches can be seamlessly inserted when port density becomes a problem. In either case, this “scale-out” of infrastructure doesn’t require any re-architecting of the network, and there is no downtime.

Building a spine-leaf architecture with Aruba CX Switching

The Aruba CX Switching Portfolio is designed for the evolving, complex demands of modern data center environments, including spine-leaf fabrics. Aruba CX switches are based on a distributed, non-blocking architecture that delivers true wired speed performance from 1GbE to 100GbE.

Aruba CX switches for spine-leaf fabrics include:

  • Aruba CX 6400: A modular 5- or 10-slot switch with up to 28Tbps capacity
  • Aruba CX 8325: A 1U switch with 1/10/25/40/100GbE connectivity ideal for leaf or spine switches
  • Aruba CX 8320: A 1U leaf switch with 10GbE server connectivity and 40GbE to the spine
  • Aruba CX 8400: A modular switch with up to 19.2Tbps capacity, ideal for spine and leaf switches where higher port density is needed

All Aruba CX switches are powered by AOS-CX, a cloud-native operating system that simplifies the management of data center networks with powerful automation, analytics, and support for live upgrades.